The present invention relates to a diagnosis system for internal combustion engines, and more particularly to a system for diagnosing failure of engine operation control systems of an engine mounted on a motor vehicle.
An electronic fuel-injection system is known of the type which is provided with a computer operable to compute various factors. Such factors may be ignition signal, throttle position, volume of intake airflow, intake manifold vacuum, coolant temperature, and oxygen concentration in exhaust gases in order which produce output signals for driving solenoid-operated injection valves. Some factors are important for engine operation and trouble in sensing systems for such important factors must be immediately warned for the safety of driving of the vehicle. Japanese patent laid open No. 51-20787 discloses a monitor system for displaying trouble in accordance with the importance of trouble which occurs. Minor trouble which does not render the engine inoperative may be diagnosed in a shop by a diagnosis system in the shop.